1. Field of the Invention
This invention relates to polymer resin tubing especially useful for catheters. More particularly, the invention relates to an ultra thin walled polymer resin flexible tubing containing a reinforcement member within the wall and which member gives the tubing a high mechanical strength, crush resistance, hydrostatic pressure capability, and radio-opacity characteristics while maintaining excellent flexibility and circular cross-section.
2. Description of the Prior Art
In general, small diameter resin tubes have been useful in the medical industry as catheters used for dispensing liquids or placing small devices into a patients vascular system. These procedures include spinal anesthesia, introduction of radio-opaque dyes into blood vessels, percutaneous transluminal coronary angioplasty and the like.
The tubes presently used in the medical field are various constructions of extruded fluoropolymers, and non-extrudable resins. These tubes are generally transparent to X-rays and other radiological techniques. For medical procedures requiring radio-opacity these tubes have been made with radiopaque resin compositions. Other tubes have been made with a metallic stylet inserted in the lumen of the tube and affixed to the ends of the tube.
Typically, fluoropolymer tubes are manufactured using a free extrusion. The fluoropolymer is extruded in the form of a hollow tube, then subjected to other processing to cure or sinter the material. This procedure yields satisfactory product, but is difficult to perform for ultra thin walls. Free extrusion of fluoropolymers with ultra thin walls can cause excessive kinking or collapse during processing.
Another method currently employed to manufacture polymer tubes is by coating a metal wire mandrel with the polymer either by extrusion or by dipping in a polymer bath. The tube is formed after the mandrel is withdrawn by elongating the wire to increase its length and decrease its diameter. The tube can then be removed by sliding it off the wire. Tubes manufactured by this technique have excellent interior diameter control. However, tubes with ultra thin wall thickness can still kink or collapse in use.
U.S. Pat. No. 4,925,710 to Buck et al. discloses an ultra thin walled sintered fluoropolymer tubing formed by coating a removable sintered fluoropolymer core and then removing such core. It is suggested that once such tubing is formed, it can be surrounded or jacketed with other layers such as braided metal or a rigid polymeric material.
Medical catheters have been manufactured from fluoropolymers such as polytetrafluoroethylene and related fluoropolymers because of their desirable physical characteristics. In U.S. Pat. No. 4,940,062 to Hampton et al., a guiding member for a catheter is disclosed, which catheter comprises an inner and an outer tube. The inner tube includes a hypotube which is limited to the proximal portion thereof. Secured to the distal end of the hypotube is a high strength polyimide tubular element lined with a lubricous material such as Teflon (polytetrafluoroethylene).
U.S. Pat. No. 4,898,577 to Badger et al. also discloses a guiding catheter with a controllable distal tip utilizing Teflon lined tubular sheath formed of braided or wound aramid fibers. The tubular sheath is surrounded by a polyethylene jacket. U.S. Pat. No. 3,734,139 to Zafiroglu discloses a composite tubing having a Teflon inner layer and a copolymer outer layer of tetrafluoroethylene and hexafluoropropylene. U.S. Pat. No. 4,051,284 to Ohkubo et at. discloses a method for producing heat resistant resin tubes by coating a metal wire with a polyimide.
U.S. Pat. No. 4,027,659 discloses a medical tube formed by extruding of a thermoplastic with an integral stripe portion which includes a powdered conducting metal or an X-ray opaque salt dispersed in the integral stripe. A medical tube made of a plastic material having an X-ray opaque pigment uniformly and homogeneously dispersed therethrough is taught in U.S. Pat. No. 3,608,555 to Greyson.
Other medical tubing made of radiopaque resin compositions are disclosed in U.S. Pat. Nos. 4,722,344, 4,469,483, 4,581,390 and 4,282,876. U.S. Pat. No. 4,796,637 discloses a catheter whose lumen includes a staff having disposed thereon or therein a predetermined number of spaced apart markings of radiopaque material.
Radiopacity, tube strength, kink resistance, crush resistance and flexibility are desirable characteristics for medical catheters. Radiopacity is desired for traceability in the body via X-Ray in procedures involving long range probing through blood vessels, etc., and for locating a catheter which has broken off while inside the body during such procedures. Tube strength is desired to decrease the possibility of catheter breakage especially during insertion and withdrawal into the vascular system. Flexibility is required for navigation of the catheter through the different passages of the vascular system for many medical procedures. Kink and crush resistance is essential for unimpeded or consistent flow rate in applications where liquids are dispensed (anesthesia, dyes, etc.) and for ease of device insertion where the tube is used as a conduit.
To give the tube these combination properties, the polymeric tubes described have been modified. By introducing a metal wire or stylet into the lumen of the tube, and securing it to or embedding it in the interior wall surface of the tube, the tube will be visible through X-ray and other radiological techniques. The stylet also increases the tensile strength of the catheter tube which helps reduce the chance of breakage during insertion and withdrawal. The size or diameter of the stylet varies, but a compromise between visibility under X-ray, strength, flexibility and fluid flow rates must be considered. To allow more cross-section under X-ray, a larger diameter stylet can be used, giving the catheter more strength, but there are disadvantages of decreased flexibility and decreased flow area of the lumen. This results in a stiffer catheter and possibly requires a larger diameter catheter to recover the flow area of the lumen. A larger diameter catheter introduces more trauma to the patient during such procedures, and therefore is less desirable. A finer diameter stylet would not affect fluid flow as much, would not affect flexibility appreciably, but its low cross-section would cause less visibility by X-ray and give the catheter less of a strength improvement. Further, the stylet inside the tube will hamper applications where devices must be passed through the tube.
Medical catheters, especially those with very thin walls, occasionally experience problems of kinking and collapse during these medical procedures. The typical solution to this problem is to increase the wall thickness to strengthen the tube. This results in a larger tube diameter (for same lumen size) and decreases flexibility, both less desirable characteristics. With a stylet attached to the inside of the tube, although kink resistance is improved, crushing of the tube remains a problem.
The instant invention provides improved mechanical strength, crush resistance, hydrostatic pressure capability and radiopacity over the prior art without a significant sacrifice of the desired physical characteristics for a medical catheter.